TARAWATCH, the group campaigning against the route of the M3 motorway in Co Meath, is to oppose efforts to establish Tara as a United Nations Educational, Scientific and Cultural Organisation (Unesco) world heritage site.
The designation is being sought by Minister for the Environment John Gormley as a means to prevent future development in the vicinity of the Hill of Tara.
Mr Gormley has retained the services of a member of the International Council on Monuments and Sites, the official advisory body to Unesco.
The decision to oppose his efforts was taken after members of TaraWatch attended a Unesco World Heritage convention in Canada recently.
The group said while Tara was "undoubtedly a site of outstanding universal value" worthy of inclusion as a world heritage site, the M3 motorway would "drastically diminish its integrity and value".
TaraWatch also said Ireland has been in breach of the Unesco World Heritage Convention since it signed the convention in 1992 because of the State's failure to nominate Tara before now.
The group is planning a number of activities to oppose the Minister's plan, and is hoping to use Heritage Week, which runs from August 24th to 31st, to highlight its campaign.
Members will also lobby Unesco to require a rerouting of the motorway before its inclusion in the list.
The group said efforts would also be made to rally international support from the World Museums Fund, the World Archaeological Congress and the European Association of Archaeologists, among others.
"We are going to take every possible action, with international support, to oppose the Minister's plan," said spokesman Vincent Salafia.